First, a conventional apparatus for examining foreign matters in through holes is described with reference to FIG. 8. Generally, examinations are conducted for through holes having diameters of several tens to several hundred micrometers to check if they are perforated in a correct number, if the sizes of the through holes are uniform, if foreign matters are present inside thereof, and the like. Normally, optical methods are used to perform the examinations described above. For example, an examination surface of a workpiece in which through holes are formed is photographed by a CCD camera through a microscope, and the result is compared with a reference value by an image processing apparatus to make an acceptance/non-acceptance judgment. In this conventional example, an auto-focus unit, a microscope, or an electron beam is required in addition to the image processing apparatus, and the examination is conducted for each of the through holes, and with an enlarged image at a high magnification.
The examination apparatus of the type described above generally has a structure shown in FIG. 8, in which a workpiece 1 having through holes formed therein is disposed at a predetermined position, a light source 2 is disposed on the side of a lower surface of the work, and an image taking device with an integral unit of a microscope unit 3 and a CCD camera 4 is disposed on the side of an upper surface of the work piece 1. The image-taking device can be elevated up and down by a z-axis automatic control mechanism 5. Also, the CCD camera 4 is connected to an image processing apparatus 7 through an auto-focus unit 6. By using this examination apparatus, the workpiece 1 having a plurality of through holes shown in FIG. 2 is photographed, in which a through hole acceptance/non-acceptance judgment is conducted based on an image taken in the unit of each of the through holes 8. For example, when a foreign matter is present in the through hole 8, the amount of passing light is reduced, and an area of the measured pixel becomes smaller. The through hole 8 having a pixel area that is smaller than a predetermined threshold value is judged as being defective.
In the apparatus for examining foreign matters in through holes described above, the diameter of each through hole is very small, and a highly magnified image is taken. As a result, a slight change in the examination conditions such as the position of the work, the camera or the like greatly affects the area value of passing light, and therefore the detection of foreign matters may not be effectively conducted. As such the examination conditions of the examination apparatus need to be well managed. Accordingly, the presence or absence of such a change in the examination conditions of the examination apparatus is judged by individually examining each of the parts of the apparatus and its examination condition.
However, in the apparatus for examining foreign matters in through holes described above, many parts of the apparatus and their examination conditions affect the size of an area value of passing light to be measured. For example, the positions and performances of the workpiece 1, the light source 2, the microscope unit 3, the CCD camera 4 and the z-axis adjusting mechanism 5 shown in FIG. 8 are all contributing factors to the size of the area value of passing light. Accordingly, substantial time and costs are required to individually examine all of the parts and their conditions, and the presence or absence of a change in the examination conditions cannot be confirmed in many occasions. This is inconvenient because the apparatus management cannot be sufficiently conducted.
In view of the inconvenience of the conventional art, it is an object of the present invention to provide a method for managing an examination of foreign matters in through holes, which can readily judge the presence or absence of a change in the examination conditions in an apparatus for examining foreign matters in through holes, and efficiently conduct the examination management.